Electrical cut-out.



E. KRAUS.

ELECTRICAL CUT-OUT. I

APPLICATION FILED Nov. 28. I9I4.

1,1 89,978. Patented July I, 1916.

- UNITED STATES PATENT EEICE.

ERNEST KRAUS, 0F LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPGRATION Ol? NEW YORK.

ELECTRICAL CUT-OUT.

Specification of Letters Patent.

Patented July 4, 191C.

To all whom t may concern Be it known that I, ERNEST Knaus, a citizen of the United States, and residing at Lynn, in the County of Essex, State of Massachusetts, have invented certain new and useful lmprovements in Electrical Cut- Outs, of which the following isa specification.

The present invention relates to the construction of devices which are selectively responsive to electrical currents at different voltages and which contain a material, suoli, for example, as boron, having a high negative temperature coeficient of resistance, the initial high resistance breaking down when the impressed voltage exceeds a certain value.

Boron is very hard and brittle and hence diflicult to shape mechanically. The' electrical characteristics of boron are such that when it is to be used in electric devices at commercial voltages thin films must be employed. For these reasons it has been found very d iflicult to mechanically shape a boron conductor which will have certain predetermined electrical characteristics and will regularly maintain these characteristics in service. y'

lt is the object of my invention toprovide an electrical cut-out device which will have a sharp break-down voltage which may be adjusted independently of the current-carrying capacity and which will regularly continue to break down at the same voltage even after continued service'. A cut-ont ot' this description may be used to automatically coinplete circuit in shunt to a device, suoli, as for example, a lamp, in a series cir- -cuit when the voltage across the terminals otl the device rises unduly, or when the device fails entirely. f l

Inaccordance with my invention a coiled lilamentary conductor consisting largely of boron is prepared by chemically depositing boron on a relatively fine filament of conductive material, such, for example, as carbon or tungsten, and electrical contact' is made on the inside and outside of this coiled filament so as to secure a unitary structure which is mechanically rugged and can be inserted in a circuit/in standard contacts.

The accompanying drawing shows in section somewhat enlarged a form of electrical cut-out embodying my invention.

In order to illustrate my invention l will describe the structural features with respect to the specific example, but of course it should be understood thatA my invention is not limited to thc specific details described. l may sta rt with a helical filament of carbon about two and one-half mils inildiameter, 'the helix lbeing about one-fourth inch in length and the turns about one-thirty-second inch apart. The diameter of the helix across the turns may be about three-tliirty-scconds of an inch. This filament is connected to a suitable current-conveying terminal and is then rendered incandescent in a mixture of boric chlorid and hydrogen. This treatment may be carried out in a. mixture of about ten parts boric chlorid and seven parts hydrogen, thc duration of treatment depending upon the properties desired in the finished cut-out. ln some cases, a gaseous compound of carbon, such as gasolene or benzol, may be added to the mixture thereby adding carbon to the boron and lowering its resistance As the carbon core may be made relatively fine, there is little tendency for subsequent change in the electrical properties of the boron by chemical combination with the core. The helical conductor l thus obtained consisting ol a core of carbon and a coating of boron is then placed upon a rod 2 of conductivc material, for example, copper or other metal, the diameter of the rod heilig so chosen that a firm contact is secured. As the boron deposited on the helix is very hard the helix may be manipulated to cut itself thrcadlike into the metal rod. A contact is securedl upon the outside ot' the boron by dipping it in molten metal, for example, lead, or in any other desired manner, securing a mass of conductive material 3 on the outside of thc boron which will not only serve as an electrical conductor but will also rigidly secure the respective parts to form a single structure. I have t'ound that even when the turns of the spiral are out of contact with each other that the molten metal will not come into contact with the inner core providing thc spaces between the turns are not too great. For convenience of insert-ing such a cutout into standard clamps metal is preferably attached to the opposite end of the conductive the structure symmetrical.

One of the main advantages of the above described form of cut-out lies in thel possibility of varying the cin'rent-earrying capacity without disturbing the structural relations of the core and shell of the boron helix. An increase in ciurent-carrying eapacity may be secured by properly choosing the dimensions of the helix and the metal parts contacting therewith, but the core upon which the boron layer is deposited need be no greater than in a cut-out of less capacity. As the core is small in all cases, the voltage at which the resistance of the boron breaks down may not only be accurately predetermined but is not likely to change by absorption oi conductive material from the core.

Although I have described the construction of the' cut-out with particular reference to boron, l wish it to be understood that my invention is also applicable to other material7 for example,` silicon, having a high coeliicient of resistance,

What I claim as new and desire to secure by Letters Patent of the United States, is

l, An electrical `cut out comprising, a helix consisting largely 4oli' boron,A a rod of conductive material making electrical conrod 2 so as to make' tact with the inner surface of said helix and .means for electrically contacting with the outer surface of said helix.

An electrical cut-out, comprising a body of conductive material7 a iilan'ientary body consisting largely of boron coiled about said body, and a mass of conductive material surrounding and rigidly binding said boron body but out of electrical contact with said core.

3. As an article of manufacture, a helical conductor having a coating ot' boron, a rod ot' conductive material contactingwith the inner surface ot said helix, and a mass of metal surrounding thc outer surface of said helix.

l. An electrical cut-out comprising a lilament having a relatively line core of conductive material and a deposit ol5 boron thereon7 electrical terminals said filament on opposite sides of the outer surface of "said boron deposit and means for maintaining said terminals spaced and out of Contact with each other.

In witness whereofa l have hereunto set my hand this 25th day ol Novemlier, i914;

ERNES KliriUS Witnesses:

' JOHN A. Mollaxns, Jr.,

.Toi-1N T. Bnncnmfn.

extending lengthwise 

